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Bio‐based "thiol‐epoxides" thermosets containing dynamic cross‐linked network topologies, permanent cross‐linking and recyclability have been successfully utilized in coatings, adhesives and composites. However, these materials typically have a low glass transition temperature and limited mechanical strength. Combining excellent mechanical properties with thermal properties remains a significant challenge. In this study, we developed a recyclable itaconic acid‐based epoxy thermoset material with high glass transition temperature and tensile strength through thiol‐olefin/thiol‐epoxy click reaction and alkyl bond radical copolymerization to construct a hybrid cross‐linked network. The tensile strength reached up to (105.9 MPa) while maintaining a high Tg (93.3°C), which is the highest value reported in the literature so far. In addition, the itaconic acid‐based epoxy has excellent recyclable processing, self‐healing properties, high hardness, solvent resistance, and surface bond strength as an adhesive and coating. The results hold potential applications in achieving sustainable development in coatings and adhesives. [ABSTRACT FROM AUTHOR]

[Display omitted] • The chemical and topological structures of flame retardant were regulated at the same time. • Modified epoxy resin showed UL-94 V0 rating and LOI above 32.6 vol% with phosphorus content of only 0.24%. • Impact strength was increased by 113% at 25°C and by 96% at −196°C after modification. • Tg was increased from 172°C for pristine resin to 194°C for modified system determined by DMA. • Flexural strength and modulus of modified epoxy were increased by 26% and 19%. Endowing epoxy resins with simultaneously improved flame retardancy, toughness and strength as well as glass transition temperature (T g) is a big challenge for us. Herein, a hyperbranched flame retardant (HBFR) with rigid backbone structure was synthesized through a facile strategy. Upon the incorporation of HBFR, the modified diglycidyl ether of bisphenol A (DGEBA) with phosphorus content of only 0.24 wt% exhibited better flame retardancy beyond expectation, showing UL-94 V-0 rating and limited oxygen index (LOI) above 32.6 vol%. Meanwhile, the modified epoxy resin demonstrated superior toughness, indicated by the more than 96% increment in impact strength both at 25 and −196°C, due to the enlarged free volume originated from hyperbranched structures. Furthermore, the T g , flexural strength and modulus of modified epoxy systems were also significantly increased because of the rigid backbone structure and high crosslinking density afforded by HBFR. This work provided us an attractive strategy for simultaneously improving the flame retardancy, toughness, T g and strength of commercial epoxy resins. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hyperbranched flame retardant was synthesized from renewable resources. • The hyperbranched flame retardant endowed epoxy resin with UL-94 V-0 rating. • The impact strength at −196 °C of modified epoxy resin was increased by114%. • The flexural strength, modulus and T g of modified epoxy resin were simultaneously improved. It is highly desired yet very challenging to overcome the flammability and brittleness of epoxy resin without compromising its glass transition temperature (T g). Herein, an epoxy-terminated hyperbranched flame retardant (EHBFR) was designed and synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and renewable protocatechualdehyde as well as guaiacol. When the synthesized EHBFR was taken to modify diglycidyl ether of bisphenol A (DGEBA), it is found that the incorporation of EHBFR remarkably improved its fire safety, endowing it with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 33.0 vol%. Meanwhile, the notched impact strength of modified DGEBA at 25 and −196 °C (quenched by liquid nitrogen) exhibited significant increment by 135% (from 3.39 to 7.97 KJ/m2) and 114% (from 2.34 to 5.01 KJ/m2), respectively. Moreover, the T g of modified epoxy resin did not show any decrease, and even increased from 172 to 194 °C when the content of EHBFR was 10 wt%, due to the synergistic effect of rigid DOPO-containing groups and high crosslink density. This work offers an efficient strategy for constructing high-performance epoxy thermosets with excellent flame retardancy, superior toughness and strength, as well as elevated T g. [ABSTRACT FROM AUTHOR]

A new strategy for the property regulation of polybenzoxazine via the regiochemistry of amide substituents was reported in this work. After the benzoxazine isomers, 2,6BAP-abz and 3,5BAP-abz, were synthesized, their chemical structures were confirmed by NMR, FT-IR and MS spectra. Then, how does the regiochemistry of amide substituent regulate the curing behaviors of benzoxazine monomers, as well as the thermal properties and flame retardancy of cured resins, poly(2,6BAP-abz) and poly(3,5BAP-abz), were investigated. Results showed that the intramolecular H-bonding involved with the ortho-CON H and O in oxazine ring in 3,5BAP-abz was much stronger than that in 2,6BAP-abz, which was responsible for its higher curing reactivity. As for the cured resin, poly(2,6BAP-abz) demonstrated higher glass transition temperature (T g) and lower surface free energy (SFE) due to the formation of more intramolecular N–H⋯N interaction between pyridine and ortho-CON H . In addition, this H-bonding was also related with the oxazole ring formation temperature and fire retardancy of poly(2,6BAP-abz) and poly(3,5BAP-abz). Overall, a deeper insight into the effect of regiochemistry on properties of polybenzoxazine was achieved. Image 1 • Selective formation of inter- or intramolecular H-bonding in PBZ was achieved through the benzoxazine isomers design. • Manipulation on the regiochemistry of amide substituent and its effect on the properties of PBZ were investigated. • It is the first time the effect of H-bonding on the polybenzoxazole formation temperature from o-amide PBZ was reported. • H-bonding was proved to have relationship with the fire resistance of o-amide PBZ due to the formation of polybenzoxazole. [ABSTRACT FROM AUTHOR]